Use type_identity to block unnecessary template argument deduction (thanks Tim Song)

include/fmt/color.h

@@ -491,10 +491,8 @@ void vformat_to(basic_memory_buffer<Char>& buf, const text_style& ts,
         internal::make_background_color<Char>(ts.get_background());
     buf.append(background.begin(), background.end());
   }
-  vformat_to(buf, format_str, args);
-  if (has_style) {
-    internal::reset_color<Char>(buf);
-  }
+  internal::vformat_to(buf, format_str, args);
+  if (has_style) internal::reset_color<Char>(buf);
 }
 }  // namespace internal
 

include/fmt/compile.h

@@ -9,6 +9,7 @@
 #define FMT_COMPILE_H_
 
 #include <vector>
+
 #include "format.h"
 
 FMT_BEGIN_NAMESPACE
@@ -549,7 +550,7 @@ std::basic_string<Char> format(const CompiledFormat& cf, const Args&... args) {
   using range = buffer_range<Char>;
   using context = buffer_context<Char>;
   internal::cf::vformat_to<context>(range(buffer), cf,
-                                    {make_format_args<context>(args...)});
+                                    make_format_args<context>(args...));
   return to_string(buffer);
 }
 
@@ -561,8 +562,8 @@ OutputIt format_to(OutputIt out, const CompiledFormat& cf,
   using char_type = typename CompiledFormat::char_type;
   using range = internal::output_range<OutputIt, char_type>;
   using context = format_context_t<OutputIt, char_type>;
-  return internal::cf::vformat_to<context>(
-      range(out), cf, {make_format_args<context>(args...)});
+  return internal::cf::vformat_to<context>(range(out), cf,
+                                           make_format_args<context>(args...));
 }
 
 template <typename OutputIt, typename CompiledFormat, typename... Args,

include/fmt/core.h

@@ -217,7 +217,7 @@
 
 FMT_BEGIN_NAMESPACE
 
-// Implementations of enable_if_t and other metafunctions for pre-C++14 systems.
+// Implementations of enable_if_t and other metafunctions for older systems.
 template <bool B, class T = void>
 using enable_if_t = typename std::enable_if<B, T>::type;
 template <bool B, class T, class F>
@@ -229,6 +229,8 @@ template <typename T>
 using remove_const_t = typename std::remove_const<T>::type;
 template <typename T>
 using remove_cvref_t = typename std::remove_cv<remove_reference_t<T>>::type;
+template <typename T> struct type_identity { using type = T; };
+template <typename T> using type_identity_t = typename type_identity<T>::type;
 
 struct monostate {};
 
@@ -1220,7 +1222,13 @@ using wformat_context = buffer_context<wchar_t>;
   such as `~fmt::vformat`.
   \endrst
  */
-template <typename Context, typename... Args> class format_arg_store {
+template <typename Context, typename... Args>
+class format_arg_store
+#if FMT_GCC_VERSION < 409
+    // Workaround a GCC template argument substitution bug.
+    : public basic_format_args<Context>
+#endif
+{
  private:
   static const size_t num_args = sizeof...(Args);
   static const bool is_packed = num_args < internal::max_packed_args;
@@ -1239,7 +1247,12 @@ template <typename Context, typename... Args> class format_arg_store {
                 : internal::is_unpacked_bit | num_args;
 
   format_arg_store(const Args&... args)
-      : data_{internal::make_arg<is_packed, Context>(args)...} {}
+      :
+#if FMT_GCC_VERSION < 409
+        basic_format_args<Context>(*this),
+#endif
+        data_{internal::make_arg<is_packed, Context>(args)...} {
+  }
 };
 
 /**
@@ -1426,9 +1439,10 @@ template <typename... Args, typename S, typename Char = char_t<S>>
 inline format_arg_store<buffer_context<Char>, remove_reference_t<Args>...>
 make_args_checked(const S& format_str,
                   const remove_reference_t<Args>&... args) {
-  static_assert(all_true<(!std::is_base_of<view, remove_reference_t<Args>>::value ||
-                          !std::is_reference<Args>::value)...>::value,
-                "passing views as lvalues is disallowed");
+  static_assert(
+      all_true<(!std::is_base_of<view, remove_reference_t<Args>>::value ||
+                !std::is_reference<Args>::value)...>::value,
+      "passing views as lvalues is disallowed");
   check_format_string<remove_const_t<remove_reference_t<Args>>...>(format_str);
   return {args...};
 }
@@ -1440,7 +1454,7 @@ std::basic_string<Char> vformat(basic_string_view<Char> format_str,
 template <typename Char>
 typename buffer_context<Char>::iterator vformat_to(
     buffer<Char>& buf, basic_string_view<Char> format_str,
-    basic_format_args<buffer_context<Char>> args);
+    basic_format_args<buffer_context<type_identity_t<Char>>> args);
 
 FMT_API void vprint_mojibake(std::FILE*, string_view, format_args);
 }  // namespace internal

include/fmt/format-inl.h

@@ -8,8 +8,6 @@
 #ifndef FMT_FORMAT_INL_H_
 #define FMT_FORMAT_INL_H_
 
-#include "format.h"
-
 #include <cassert>
 #include <cctype>
 #include <climits>
@@ -17,6 +15,8 @@
 #include <cstdarg>
 #include <cstring>  // for std::memmove
 #include <cwchar>
+
+#include "format.h"
 #if !defined(FMT_STATIC_THOUSANDS_SEPARATOR)
 #  include <locale>
 #endif
@@ -1380,7 +1380,8 @@ FMT_FUNC void vprint(std::FILE* f, string_view format_str, format_args args) {
 FMT_FUNC void internal::vprint_mojibake(std::FILE* f, string_view format_str,
                                         format_args args) {
   memory_buffer buffer;
-  vformat_to(buffer, format_str, basic_format_args<buffer_context<char>>(args));
+  internal::vformat_to(buffer, format_str,
+                       basic_format_args<buffer_context<char>>(args));
   fwrite_fully(buffer.data(), 1, buffer.size(), f);
 }
 #endif

include/fmt/format.h

@@ -33,8 +33,6 @@
 #ifndef FMT_FORMAT_H_
 #define FMT_FORMAT_H_
 
-#include "core.h"
-
 #include <algorithm>
 #include <cerrno>
 #include <cmath>
@@ -43,6 +41,8 @@
 #include <memory>
 #include <stdexcept>
 
+#include "core.h"
+
 #ifdef __clang__
 #  define FMT_CLANG_VERSION (__clang_major__ * 100 + __clang_minor__)
 #else
@@ -3228,7 +3228,7 @@ std::basic_string<Char> to_string(const basic_memory_buffer<Char, SIZE>& buf) {
 template <typename Char>
 typename buffer_context<Char>::iterator internal::vformat_to(
     internal::buffer<Char>& buf, basic_string_view<Char> format_str,
-    basic_format_args<buffer_context<Char>> args) {
+    basic_format_args<buffer_context<type_identity_t<Char>>> args) {
   using range = buffer_range<Char>;
   return vformat_to<arg_formatter<range>>(buf, to_string_view(format_str),
                                           args);
@@ -3238,7 +3238,7 @@ template <typename S, typename Char = char_t<S>,
           FMT_ENABLE_IF(internal::is_string<S>::value)>
 inline typename buffer_context<Char>::iterator vformat_to(
     internal::buffer<Char>& buf, const S& format_str,
-    basic_format_args<buffer_context<Char>> args) {
+    basic_format_args<buffer_context<type_identity_t<Char>>> args) {
   return internal::vformat_to(buf, to_string_view(format_str), args);
 }
 
@@ -3262,8 +3262,9 @@ template <typename S, typename OutputIt, typename... Args,
           FMT_ENABLE_IF(
               internal::is_output_iterator<OutputIt>::value &&
               !internal::is_contiguous_back_insert_iterator<OutputIt>::value)>
-inline OutputIt vformat_to(OutputIt out, const S& format_str,
-                           format_args_t<OutputIt, char_t<S>> args) {
+inline OutputIt vformat_to(
+    OutputIt out, const S& format_str,
+    format_args_t<type_identity_t<OutputIt>, char_t<S>> args) {
   using range = internal::output_range<OutputIt, char_t<S>>;
   return vformat_to<arg_formatter<range>>(range(out),
                                           to_string_view(format_str), args);
@@ -3289,7 +3290,7 @@ inline OutputIt format_to(OutputIt out, const S& format_str, Args&&... args) {
   internal::check_format_string<Args...>(format_str);
   using context = format_context_t<OutputIt, char_t<S>>;
   return vformat_to(out, to_string_view(format_str),
-                    {make_format_args<context>(args...)});
+                    make_format_args<context>(args...));
 }
 
 template <typename OutputIt> struct format_to_n_result {
@@ -3317,7 +3318,7 @@ template <typename OutputIt, typename Char, typename... Args,
           FMT_ENABLE_IF(internal::is_output_iterator<OutputIt>::value)>
 inline format_to_n_result<OutputIt> vformat_to_n(
     OutputIt out, std::size_t n, basic_string_view<Char> format_str,
-    format_to_n_args<OutputIt, Char> args) {
+    format_to_n_args<type_identity_t<OutputIt>, type_identity_t<Char>> args) {
   auto it = vformat_to(internal::truncating_iterator<OutputIt>(out, n),
                        format_str, args);
   return {it.base(), it.count()};
@@ -3339,7 +3340,7 @@ inline format_to_n_result<OutputIt> format_to_n(OutputIt out, std::size_t n,
   internal::check_format_string<Args...>(format_str);
   using context = format_to_n_context<OutputIt, char_t<S>>;
   return vformat_to_n(out, n, to_string_view(format_str),
-                      {make_format_args<context>(args...)});
+                      make_format_args<context>(args...));
 }
 
 template <typename Char>

include/fmt/printf.h

@@ -597,7 +597,8 @@ inline format_arg_store<wprintf_context, Args...> make_wprintf_args(
 
 template <typename S, typename Char = char_t<S>>
 inline std::basic_string<Char> vsprintf(
-    const S& format, basic_format_args<basic_printf_context_t<Char>> args) {
+    const S& format,
+    basic_format_args<basic_printf_context_t<type_identity_t<Char>>> args) {
   basic_memory_buffer<Char> buffer;
   printf(buffer, to_string_view(format), args);
   return to_string(buffer);
@@ -616,12 +617,13 @@ template <typename S, typename... Args,
           typename Char = enable_if_t<internal::is_string<S>::value, char_t<S>>>
 inline std::basic_string<Char> sprintf(const S& format, const Args&... args) {
   using context = basic_printf_context_t<Char>;
-  return vsprintf(to_string_view(format), {make_format_args<context>(args...)});
+  return vsprintf(to_string_view(format), make_format_args<context>(args...));
 }
 
 template <typename S, typename Char = char_t<S>>
-inline int vfprintf(std::FILE* f, const S& format,
-                    basic_format_args<basic_printf_context_t<Char>> args) {
+inline int vfprintf(
+    std::FILE* f, const S& format,
+    basic_format_args<basic_printf_context_t<type_identity_t<Char>>> args) {
   basic_memory_buffer<Char> buffer;
   printf(buffer, to_string_view(format), args);
   std::size_t size = buffer.size();
@@ -644,12 +646,13 @@ template <typename S, typename... Args,
 inline int fprintf(std::FILE* f, const S& format, const Args&... args) {
   using context = basic_printf_context_t<Char>;
   return vfprintf(f, to_string_view(format),
-                  {make_format_args<context>(args...)});
+                  make_format_args<context>(args...));
 }
 
 template <typename S, typename Char = char_t<S>>
-inline int vprintf(const S& format,
-                   basic_format_args<basic_printf_context_t<Char>> args) {
+inline int vprintf(
+    const S& format,
+    basic_format_args<basic_printf_context_t<type_identity_t<Char>>> args) {
   return vfprintf(stdout, to_string_view(format), args);
 }
 
@@ -667,12 +670,13 @@ template <typename S, typename... Args,
 inline int printf(const S& format_str, const Args&... args) {
   using context = basic_printf_context_t<char_t<S>>;
   return vprintf(to_string_view(format_str),
-                 {make_format_args<context>(args...)});
+                 make_format_args<context>(args...));
 }
 
 template <typename S, typename Char = char_t<S>>
-inline int vfprintf(std::basic_ostream<Char>& os, const S& format,
-                    basic_format_args<basic_printf_context_t<Char>> args) {
+inline int vfprintf(
+    std::basic_ostream<Char>& os, const S& format,
+    basic_format_args<basic_printf_context_t<type_identity_t<Char>>> args) {
   basic_memory_buffer<Char> buffer;
   printf(buffer, to_string_view(format), args);
   internal::write(os, buffer);
@@ -683,9 +687,9 @@ inline int vfprintf(std::basic_ostream<Char>& os, const S& format,
 template <typename ArgFormatter, typename Char,
           typename Context =
               basic_printf_context<typename ArgFormatter::iterator, Char>>
-typename ArgFormatter::iterator vprintf(internal::buffer<Char>& out,
-                                        basic_string_view<Char> format_str,
-                                        basic_format_args<Context> args) {
+typename ArgFormatter::iterator vprintf(
+    internal::buffer<Char>& out, basic_string_view<Char> format_str,
+    basic_format_args<type_identity_t<Context>> args) {
   typename ArgFormatter::iterator iter(out);
   Context(iter, format_str, args).template format<ArgFormatter>();
   return iter;
@@ -705,7 +709,7 @@ inline int fprintf(std::basic_ostream<Char>& os, const S& format_str,
                    const Args&... args) {
   using context = basic_printf_context_t<Char>;
   return vfprintf(os, to_string_view(format_str),
-                  {make_format_args<context>(args...)});
+                  make_format_args<context>(args...));
 }
 FMT_END_NAMESPACE
 

test/format

@@ -83,9 +83,9 @@ namespace std {
     Out format_to(Out out, wstring_view fmt, const Args&... args);
 
   template<class Out>
-    Out vformat_to(Out out, string_view fmt, format_args_t<Out, char> args);
+    Out vformat_to(Out out, string_view fmt, format_args_t<fmt::type_identity_t<Out>, char> args);
   template<class Out>
-    Out vformat_to(Out out, wstring_view fmt, format_args_t<Out, wchar_t> args);
+    Out vformat_to(Out out, wstring_view fmt, format_args_t<fmt::type_identity_t<Out>, wchar_t> args);
 
   template<class Out>
     struct format_to_n_result {
@@ -730,17 +730,17 @@ wstring vformat(wstring_view fmt, wformat_args args);
 template<class Out, class... Args>
   Out format_to(Out out, string_view fmt, const Args&... args) {
     using context = basic_format_context<Out, decltype(fmt)::value_type>;
-    return vformat_to(out, fmt, {make_format_args<context>(args...)});
+    return vformat_to(out, fmt, make_format_args<context>(args...));
   }
 
 template<class Out, class... Args>
   Out format_to(Out out, wstring_view fmt, const Args&... args) {
     using context = basic_format_context<Out, decltype(fmt)::value_type>;
-    return vformat_to(out, fmt, {make_format_args<context>(args...)});
+    return vformat_to(out, fmt, make_format_args<context>(args...));
   }
 
 template<class Out>
-  Out vformat_to(Out out, string_view fmt, format_args_t<Out, char> args) {
+  Out vformat_to(Out out, string_view fmt, format_args_t<fmt::type_identity_t<Out>, char> args) {
     using range = fmt::internal::output_range<Out, char>;
     detail::format_handler<detail::arg_formatter<range>, char, basic_format_context<Out, char>>
       h(range(out), fmt, args, {});
@@ -749,7 +749,7 @@ template<class Out>
   }
 
 template<class Out>
-  Out vformat_to(Out out, wstring_view fmt, format_args_t<Out, wchar_t> args);
+  Out vformat_to(Out out, wstring_view fmt, format_args_t<fmt::type_identity_t<Out>, wchar_t> args);
 
 template<class Out, class... Args>
   format_to_n_result<Out> format_to_n(Out out, iter_difference_t<Out> n,